The United Nations said Russia has agreed to a 48-hour humanitarian cease-fire in the divided Syrian city of Aleppo to allow aid deliveries, but security guarantees are needed from other parties in the conflict.

The UN has pushed for a weekly 48-hour pause in fighting in Aleppo to alleviate suffering for about 2 million people. But with Russia and other major powers back opposing sides in Syria's five-year civil war, carrying that out has proved difficult.

"We have...agreement now from the Russian Federation for the 48-hour pause. We're waiting [for] it from the other actors on the ground. That has taken more time frankly than I thought was needed," Jan Egeland, who chairs the UN humanitarian task force, told reporters on August 25.

UN Special Envoy for Syria Staffan de Mistura, echoed his comments.

Russia is the main backer of Syrian President Bashar al-Assad. Rebel groups opposing Assad are supported by Western and Gulf powers.

The U.S. State Department said while Washington backs the 48-hour Aleppo cease-fire, it is focused on achieving a broader country-wide cessation of hostilities.